Recognize metamerism
Let us first introduce two metamerism phenomena.
Phenomenon 1: In real life, when shopping in malls and supermarkets, socks or gloves with the same color under the fluorescent light, but after buying it, the color is different under the incandescent light.
Phenomenon 2: In color printing, the color of the prints approved by the printing plant and customers during the trial printing is found, but when the materials, equipment and operation technology are unchanged, when it is printed in large quantities, it is found that under the new observation environment The color of the printed product has deviations, sometimes even a large color difference, which affects the quality of the print. This will cause users to doubt the authenticity of the goods, and even demand return, which will affect the reputation of the printing plant.
The metamerism phenomenon is simply the same color, but different spectral composition. The reproduction of a color has a certain relationship with the characteristics of the light source observing the color. A certain two substances show the same color under one light source, but they show different colors under another light source. This phenomenon is called the same color. Heterogeneous phenomenon.
Only by fully understanding the characteristics, production principles and control factors of metamerism can we effectively avoid its negative impact on print quality. At the same time, we should also make full use of the unique phenomenon of metamerism and apply it to packaging The field of anti-counterfeiting printing.
Anti-counterfeiting principle of same color heterogeneous ink
The same color heterogeneous ink is a new type of ink with unique anti-counterfeiting function. Metamerism inks are developed based on the principle of metamerism of substances. Under the sunlight, the two metachromatic inks have the same visual effect, that is, they have the same color characteristic expression value, but the spectral characteristics of the two inks are different. Two pigments with the same color and different spectral characteristics are used to produce two inks with the same color effect and different spectral characteristics, and become a pair of homochromatic and heterogeneous inks. The anti-counterfeiting function of the same color heterogeneous ink mainly depends on the different absorption and reflection ability of the pigment in the ink that plays a role in color development.
Two kinds of metamerism inks reflect the hue and contrast on the surface under a certain illumination light, and their colors and contrast will be significantly different under the other illumination light. According to this principle, we can use two metamerism inks to print metamerism images to achieve anti-counterfeiting purposes. The anti-counterfeiting metamerism image is composed of foreground pixels and background pixels that are indistinguishable under daylight illumination, and the color difference between the foreground pixels and the background pixels is displayed under another different illumination.
The metamerism of the two inks originates from the fact that they have almost the same spectrum in the highly sensitive visible spectrum of the human eye, while the spectral difference in the infrared or ultraviolet region of the human eye is very different. Under daylight lighting, the colors of the two inks are almost indistinguishable, but when viewed with a filter such as a red filter, the color difference between the two inks can appear.
The anti-counterfeiting effect of the same color heterogeneous ink is obvious, and it is easy to observe. Because special pigments are needed for production, its anti-counterfeiting security is better. The metachromatic ink has good durability, stable performance, no decay cycle problem, and color rendering characteristics will not change for a long time.
Two methods can be used to distinguish the same color and different spectrum ink. First, according to the different spectral characteristics of the ink, the spectrum of the two inks is measured by the instrument to compare and distinguish. The second is based on the principle that the ink has selective absorption and reflection of light, and is observed through a specific color filter. One ink changes the reflected light due to the role of the color filter, while the other ink still absorbs and reflects the original The color of the light has not changed.
Application of Same Color Different Spectrum Ink in Anti-counterfeiting Printing
Since the metamerism images are specially designed for the human eye and not for the replication system, there is nothing special about the printing method of metamerism inks. The printing of the same color and heterogeneous ink is mostly offset printing, which can be printed by color separation or normal printing. The two inks should be printed on the adjacent parts of the substrate for easy observation and comparison.
The same color heterogeneous ink can also be used in combination with infrared ink, the anti-counterfeiting effect is better. The characteristic of this application is that under the illumination of the wavelength of 600-1000mm, the two inks have the same visual effect, and under the infrared light, the two inks have different colors and different spectral characteristics, which can achieve double anti-counterfeiting efficacy. For example, when printing, you can use infrared invisible ink to cover the infrared visible bar code, so that the human eye can only see the visible color block and the bar code under natural light, and the bar code under the ink cover layer can be scanned with near infrared bar code仪 读。 Instrument reading. Since the overwritten barcode cannot be copied during copying, it cannot be forged. As another example, we can use a kind of infrared invisible ink to cover the printing design of green pixels. Under daylight lighting, the green pixels are not visible. Observe the print through the red or magenta filter. Since the filter absorbs green light, the green pixel becomes black. And because the red light passes through the filter, the red image becomes brighter. This contrasts the foreground and background colors.
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